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UNITED STATES PATENT Ormea..

FRANK J. SPRAGUE, OF NEYV YORK, N. Y., ASSIGNOR TO THE SPRAGUE ELECTRICRAILWAY AND MOTOR COMPANY.

METHOD OF OPERATING ELECTRICHRALNAY TRAlNS.

SPECIFICATION forming part of Letters Patent No. 318,668, dated May 26,1885.

Application filed December 22, 1884.

To all whom it may concern:

Be it known that I, FRANK J. Srnnenn, of New York, in the' county andState of New York, have invented a certain new and useful Improvement inMethods of Operating Electric-Railway Trains, of which the following isa specification.

The object of my invention is to provide an effective method of brakingor slowing down a train on an electric railway, which shall not entailthat loss of energy incurred in the methods of braking which haveheretofore been used or proposed both in steam and electric railways.This method consists in changing the electro-dynamic motor whichreceives current from the line and propels the train into adynamo-electric generator receiving energy from the momentum of thetrain and giving current to the line, and under perfect control to Varythebraking-power. Therefore instead, as in the case of a mechanicalbrake, of using energy to stop or slow down the train, by my inventionsuch act of stopping or slowing down gives current to the line andrelieves the generating-stations by furnishing additional power to themotors of other ltrains.

In my application Serial No. 121,487 is set forth a method of varyingthe mechanical effeet-s in an electrodynamic motor by an inverse varyingof the strength of the fieldmagnets of the motor. My method of changingthe railway-motor into a generator is based upon the same principle. Bya continued in- /erease of field strength I decrease, and finallyreverse, the mechanical effects of the motor.

Vhen the machine is running 'as a motor, it develops a certain counterelectro-motive force, which, taken with theinitial electro-motive force,determines the effective electronictive force, and hence thearmature-current. This counter electro-motive force depends upon thestrength of field and the velocity of the armature, and is independentof everything else. It is evident, therefore, that if the strength ofthe iieldmagnet is increased the counter electro-motive force is alsoincreased, and if 'the increase of eld is continued the initial andcounter electro-motive forces will become equal, and then the counterelectro-motive force will predominate. The

(No model.)

machine has now become a generator and gives current to the line and itsmechanical effects are reversed, so that it brakes the tra-in instead ofpropelling it, and the current generated by it and the braking-power orreversed mechanical effect are now controllable by further increas` ingor by rediminishing the strength of field.

It will be seen that mechanical energy is received by the reversed motoraccording to the mass of the train and its velocity. If a train shouldstart on a downgrade unprovided with a brake, the energy of fallingwould tend to increase its speed, but when my method ot' braking is usedthis mechanical energy is transformed in the machine into electricalenergy delivered to the line, and augmenting that supplied from thegenerating-stations to the other trains, which may be moving uponnpgrades or on levels.

Then it is desired to slow down a train on a level grade, the field isincreased, as before, until the counter electro-motive forcepredominates over the initial, and the energy stored up in the movingtrain is exerted to run the machine as a braking-dynamo. As the trainslows, however, the diminution of speed of the armature will tend todiminish the coun ter electro-motive force, and the increase of eldstrength must therefore be continued, so as to still maintain thecounter electro-motive force above the initial and keep the machinerunning as a generator as long as pincticablf.A when other methods ofbreaking, to be set forth in another application, may be used ifnecessary.

I will give an instance t0 show how effectively my invention may beemployed, premising that when large masses of iron are used in thetieldanagnets the strength of the eld can be varied within effectivelimits four or iivc hundred per cent., and also that a well constructedarmature can carry for a short time iifty, seventy-five, or perhaps,feven one hundred per cent. more current than it can stand for any longrun. Suppose the armature of the motor in question to have a resistanceof three-tenths of an ohm, with its held-magnet in shunt relation to itsarmature (which is always the preferable manner of connection) andprovided with suitable means for varying ICO its strength. Suppose theinitial electro-motive force to be five hundred volts, and fortyhorse-power to be required from the motor when running at its maximum.Allowing for losses in conversion this forty horse -power would be aboutthirtytwo thousand watts. The counter electro-motive force would be fourhundred and eighty volts, the effective electromotive force twentyvolts, and the current sixty-seven ampres. rlhe electrical efficiency ofthe armature would be ninetyeix per cent. Suppose the strength of theiield to be increased about four per cent.,vthe speed remaining thesame, the motor running ona downgrade, the counter electro-motive willbe increased to five hundred volts,and the motor-armature will then beperfectly passive electrically, neither taking from or giving to theline. Let the field strength be increased again one per cent., and lettheincrease be continued in the same ratio. The result is shown in thefollowing table:

Approximate energy re quired from train, allowingr for losses.

Total eldinorease. Current to line.

5 per cent. 13.3 ampres. 9.5 horse-power. fr 29.3 20.5) '7 45.3 32.7 861.3 44.7 S) 77.3 56.9 l0 93.3 69.3

From the above it will be seen that by sim ply increasing the fieldstrength one twentyiifth part, the machine is converted from a motordriving a train with forty horse-power of effective work to aperfeetlypassive machine, allowing the train to run absolutely free, Then 'byincreasing the iicld one one-hundredth part themotor at once exerts apositive braking force, and on an increase of about eight and one-halfper cent. above its original strength it will give back to theline-current equal to that which was originally taken from itsufficient, evidently, to run some other motor of the system which mayat that time require that amount of current, and by increasing theoriginal field ten per cent. the machine acts as a dynamo, requiringmore than fifty per cent. more energy than is demanded to run it as amotor developing forty horsepower.

This method of braking, it will be seen, is under perfect control, andit is the most economical system possible for an electric railway, sincewhenever a train descends a grade and whenever a train stops the energystored up in the moving train is delivered` in the form of electricalenergy upon the line. rlhis advantage is most readily appreciable bycomparing the action of my invention' with that which occurs on asteam-railway train. Suppose it to be ascending a grade, then the engineexerts more than its average amount of power. lVhen it reaches the topand enters upon a downgrade steam is shut off, and when the train beginsto run faster than is desired steam is admitted to the vacuumbrakeejector, pressure is applied to the trucks, and the energy of the trainis then converted into heat on the rims of the wheels and on thebrake-shoes. In other words, all the energy in excess of that necessaryto run the train on a level which has been required to climb the gradeis now thrown away in going down the grade, instead of being utilized,as in my system; and, furthermore, additional steam is actually requiredto check the tendency to augmented speed. Then when the train approachesa stopping-place, or wherever it is necessary to slow the train downquickly,steam has to be employed to actuate the brakes, and all thisadditional power is simply thrown away. By my method of working thegreaterl part of this loss is'cntirely obviated.

It is true that not all of the energy will be converted intoelectricity; but alarge proportion of it will be.

On a double-track road with both tracks supplied from the same maincircuit, as set forth in other applications made by me, the energy givento one track is also communicated to the other. rlhe upgrades on onetrack being always balanced by the downgrades on the other track, it isevident that the total upgrade of the whole systemis equal to the totaldowngrade thereof. Therefore, energy being expended on the upgrades andgiven out to nearly the same extent on the downgrades, the energyrequired in the system is that sufficient to move a train upon a levelwith a slight percentage added; but on asteamrailway the energy requiredis not only that sufficient to run a train on a level, but, in addition,thatnecessary to raise it from the lower to the higher grades on bothtracks, no matter how many of such grades there may be.

I may employ any effective method for varying the strength ot' theiield. I may employ adjustable resistance, or maycut in and out sectionsofthe field-coils, or reverse the current in a greater or less number ofsaid coils. l prefer, however, to employ such methods as have been setforth in my prior applications relating tothe regulation ofelectro-dynamic motors.

The accompanying drawing represents an electric-railway system in whichmy invention is employed.

A A and B B are respectively the two tracks of an electric railway.rIhere are two sets of workingconductors, a u and b Z), preferablydivided into sections, from which the motors C and C derive current, andsuch work ing-conductors are connected by branch conductors c @with thecontinuous main conductors P N, which extend the whole length of theline and receive current from the generatingstations atD D bysupply-conductorspa. .The working-conductors, instead of beingintermediate rails of the track, maybe wires placed overhead or by theside ofthe track, or in any position where the motor can receive currentfrom them, or 'the main rails of the track may form one or both sides ofthe working-circuit.

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The main conductors may be placed overhead or underground, or in anyconvenient position.

In the form shown the motors have contactwheels e e on one side and f fon the other, which travel on and take current from theworking-conductors.

E is the armature, F F the held-magnet, and Gr the commutator, of cachmotor. Each motor which travels upon the line is provided with suitablemeans for regulating its iicldmagnet strength.

As shown, connections g g from different points of the main ield-coilsextend to contact-blocks of a circular commutator, h.. From one limb ofthe magnet they extend to one side of the commutator and from the otherlimb to the other. An independent field-coil, 7c 7c, has its terminalsconnected to the arinsl Z, which are insulated from each other, and arepivoted at m. Portions of these arms are broken away in the drawing.

It will be seen that the independent coil is thus in a shunt between thetwo sets of main coils, and by moving` the arms Z Zsaid independent coilis shunted around a greater or less number of the sections of maineld-coi1s, and thereby the magnetizing effect of said independent coiland the strength of the field is varied, or by a continued movement ofthe arms the current of the independent coil is reversed, so that itopposes the main field coils with a strength variable at will.

The terminals of the armature are preferably connected to arms n n oncommutator h, whereby the armaturecurrent may be varied or reversed inthe same manner as the independent eld-coils when so desired.

It is evident that the use of my invention is not confined to adouble-track road or to a road in which main conductors are used tosupply working-conductors, for my method of braking is applicable to anyelectric-railway system which has been used or proposed.

l/Vhat I claim is- 1. The method herein described of braking anelectric-railway train, which consists in increasing the counterelectro-motive force of the motor propelling the train until it exceedsthe initial electro-motive force on the line.

2. The method herein described of braking an electric-railway train,consisting in increasing the strength of the iield-magnet of the motorpropelling the train until the counter electro-motive force developed byits armature exceeds the initial -electro-motive force on the line.

3. The method of operating electric railways herein described, whichconsists in increasing the counter electro-motive force of each motorwhen slowing down until it exceeds the initial electro-motive force onthe line.

4. The method or" operating electric railways herein described, whichconsists in in- 65 creasing the counter electro-motive force of eachmotor when running on a downgrade until it exceeds the initialelectro-motive force on the line.

5. The method herein described of maintaining the counter electro-motiveforce of an electric-railway motor above the initial when the train isslowing down, which consists in increasing .the strength of thefield-magnet of the motor as the speed of the train slackens.

6. The method herein described of slowing down or stopping anelectric-railway train, which consists in increasing the strength of thefield-magnet of the motor propelling the train until the counterelectro-motive force of the armature exceeds the initial electro-motiveforce on the line, and then further increasing` the said field-magnetstrength to maintain the counter electro-motive force above the initialas the speed of the train slackens. 8

This specification signed and witnessed this 12th day of December, 1884.

FRANK J. SPRAGUE.

Vitnesses:

T. G. GREENE, Jr., E. C. RowLAND.

